The present invention relates to optical tracking systems and, in particular, it concerns a system and method for optical position measurement and guidance of a rigid or semi-flexible tool to a target.
Needle tools are often used in the medical field to deliver local treatment. In recent years, these procedures are carried by interventional radiologists, physicians who are experts in using imaging devices for guiding and controlling diagnostics and therapeutic procedures. In these procedures, the needles are inserted into the body under control of the imaging device.
Since the energy used by CT and fluoroscopy is X-ray, which is ionizing and harmful to living organs, image guided systems have been developed for navigating tools to a target based on preoperative CT data. Such navigation systems measure the location of the body and the location of the tool in six degrees of freedom and, by subtracting tool location from body location, determine the location of the tool relative to the body. At the beginning of the procedure, the CT data and the body are registered to match their coordinates. This is done by matching at least three fiducial points identified in the CT data and also in the body. In most such systems, one of two types of technology is used to determine the location of the tool and the body, that is: optical trackers and electromagnetic trackers. In optical trackers, the system makes use of two spaced apart video cameras and, by monitoring three or more identifiable light sources mounted on the tracked object, calculates the location and orientation of the object in up to six degrees of freedom (6 DOF) through triangulation calculations. In electromagnetic trackers, a transmitter having a plurality of antennae transmits a plurality of quasi-static magnetic fields. A receiver having a plurality of antennae receives these signals, and based on these signals calculates the location of the receiver relative the transmitter.
In these systems, the positions of both the tool and the body are determined relative to an intermediate reference system of coordinates, which is external to both the tool and the body. In the case of electromagnetic systems, the reference coordinates are defined by the transmitting antennae. In the optical trackers, the reference coordinates are defined by the camera. Subtracting the coordinates of the tool from that of the body yields the direct location of the tool in body coordinates. Since each position determination inherently adds some location error to the process, using an intermediate system of coordinate in determination of the position of the tool relative to the body is less accurate than could possibly be achieved by direct measurement of the position of the tool in body system of coordinates.
U.S. Pat. No. 6,216,029 to Paltieli describes free-hand directing of a needle towards a target located in a body volume. In this patent, the imaging device is a hand held ultrasound scanner. Electromagnetic location sensors are implemented in the transducer as well as in the handle of the tool. Both locations are determined relative to a reference coordinates frame defined by the electromagnetic tracking system.
The above described image guided systems are design to guide rigid tools to a target. However, needles, because of their small diameters tend to bend. Particularly when pushed percutaneously towards a target, the forces applied to manipulate and advance the needle often cause deflection. Since the location sensors in the aforementioned systems are attached to the proximal part of needle, measuring the orientation of the proximal portion without compensating for the deflection of the needle results in an erroneous location determination of the needle's distal tip. Consequently, the prediction of its path to the target will also be wrong.
Many of the internal organs of the body are covered by membranes such as pleura and peritoneum. These membranes are held in place by vacuum forces between the membrane and the outer organs. If the membrane is punctured, air leaks into the interspace between the membrane and the outer organ, causing the membrane to sink. In the lung this phenomenon is called Pneumothorax, and is very common, occurring in about 30% of the procedures of percutaneous thoracic needle biopsy.
There is therefore a need for a system and method for optical position measurement and guidance of a rigid or semi-flexible tool to a target which would measure the position of the tool directly in a set of coordinates fixed with the body. It would also be advantageous to provide a system and method for guiding a needle to a target including compensation for the deflection of the needle. Such a system would be expected to be highly advantageous for avoiding complications such as Pneumothorax.